New University Based SRF Materials Research Efforts (in the US)

Transcription

1 New University Based SRF Materials Research Efforts (in the US) Pierre Bauer, Tsuyoshi Tajima, Anne-Marie Valente Snowmass 2005 Materials R&D / WG5 08/18/2005 P. Bauer Materials R&D section WG5 - Snowmass Conference

2 LCRD Proposals Funded: P.Lee: D.N. Seidman: L.Vuskovic: Magnetic Investigation of High Purity Niobium for Superconducting RF Cavities, new proposal, DOE 3D Atom-Probe Microscopy on Niobium for SRF Cavities new proposal, DOE Investigation of Plasma Etching for Superconducting RF Cavities surface Preparation, new proposal, DOE Not funded: R. Schill: Investigation of Secondary Electron Emission from Nb Surfaces with Different Surface Treatments, new proposal V.Nesterenko: D.N. Seidman: Evaluation of MgB2 for Future Accelerator Cavities, new proposal Experimental Study of High Field Limits of RF Cavities, new proposal 08/18/2005 P. Bauer Materials R&D section WG5 - Snowmass Conference

3 Magnetic Flux Penetration Fnal / University of Wisconsin Magneto-optical measurements show clear evidence of pre-mature flux penetration into samples via the grain boundary. Example below: large grain material from JLab before processing. HTSC Zero field cooled (ZFC) to the superconducting state, then field applied. M Top Surface Light Image ZFC T=5.6 K H=8.4 mt 3D Model of GB 08/18/2005 P. Bauer Materials R&D section WG5 - Snowmass Conference

4 Mixed Josephson/Abrikosov vortex penetration bulk superconductor H-field penetration weak superconductor H(t) mixed vortex E(t) J d,weak λ J d,bulk H<<H c1,weak J<<J d,weak H<H c1,weak J<J d,weak H>H c1,weak J>J d,weak 08/18/2005 P. Bauer Materials R&D section WG5 - Snowmass Conference

5 Other Activities University of Wisconsin Microscopy and related material characterization (surface roughness, metallurgical, crystallo-graphical, chemical,..) Theoretical work by A. Gurevich: hot spot model Non-linear BCS resistance Thermal Feedback model H(t) Quality factor (TESLA 1-cell) 1.E+12 1.E+11 1.E+10 CEA C K before/after bake lin. BCS only, k=7.6, h=1780 w. non-lin. BCS corr. (C~3.5, H c =180mT) k=7.6, h= E+09 coolant Peak RF field (mt) 08/18/2005 P. Bauer Materials R&D section WG5 - Snowmass Conference

6 UW mid-term program Achievements: Evidence of pre-mature flux penetration through GBs; (Mixed Abrikosov-Josephson flux lines a la Gurevich) Mid-term program: Disentangle topology from chemistry Measure grain boundary Hc, Jd Understand defects other than GB Theoretical support surface resistance contribution from vortex penetration,..etc! P. Lee 08/18/2005 P. Bauer Materials R&D section WG5 - Snowmass Conference

7 3D atomic probe at NU / Fnal First results: Smooth transition from Nb 2 O 5 to Nb with 5-10% interstitial O, ~20 nm oxide 08/18/2005 P. Bauer Materials R&D section WG5 - Snowmass Conference

8 NU - mid-term program Oxide composition/thickness Interstitial elements in bulk (H is a problem) Nano-chemistry of grain-boundaries EP, BCP Fine grain - single crystal Bakes,..etc 08/18/2005 P. Bauer Materials R&D section WG5 - Snowmass Conference

9 JLab/ODU Plasma-Etching A.M. Valente / L. Vuskovic: Plasma-etching: Takes place under vacuum. Allows control on the final oxidation phase Allows the possibility to avoid final oxidation 1) plasma oxidation in Ar-O after plasma etching (stable surfaces with a much higher pentoxide to suboxide ratios?) 2) dielectric layers Combines well w. other JLab programs: L. Phillips: TE011 cavity G. Wu: Plasma Coating 3) thin superconducting layers;- i.e. NbN which is quite stable in the presence of air. 08/18/2005 P. Bauer Materials R&D section WG5 - Snowmass Conference

10 Another Gurevich Idea A. Gurevich 08/18/2005 P. Bauer Materials R&D section WG5 - Snowmass Conference

11 LANL/UC MgB2 Development T. Tajima / STI / Padamsee / Geng / Romanenko: 08/18/2005 P. Bauer Materials R&D section WG5 - Snowmass Conference

12 ANL/NU Field Emission Atom Probe samples look like field emission (breakdown) sites. Atom Probe work is useful for two reasons: 1) It provides a detailed look at high electric field on materials. 2) It provides a way of looking at surface composition. Emitter in Cavity Atom Probe Sample Surface field 4 8 GV/m 4 40 GV/m Size ~100 nm ~100 nm Temperature 300+ K K Pulsing MHz 0.2 MHz Stored energy J < 10-6 J J. Norem / D. Seidman / J. Sebastian / K. Yoon: 08/18/2005 P. Bauer Materials R&D section WG5 - Snowmass Conference

13 We need more university involvement! Chemical analysis (3DAP, XPS, SIMS, AES, ) Superconducting properties (magnetization, STM, SQUID microscopy,.) Low and high power RF properties (sample in host cavity tests, microwave microscopy,??) Microscopy, surface roughness Defect detection ECS, SQUID-ECS,.. More ideas?? 08/18/2005 P. Bauer Materials R&D section WG5 - Snowmass Conference

14 MSU Thermal Properties A. Aizas, T. Grimm: Kapitza and κ measurements Thermal conductivity of Niobium Samples 1 & 2 K (W/cm/k) Av. Temperature (K) smp 2 smp 1 08/18/2005 P. Bauer Materials R&D section WG5 - Snowmass Conference

15 MSU Mechanical Properties H. Jiang, T. Bieler: mechanical properties, formability, texture, creep Next: single crystal material 08/18/2005 P. Bauer Materials R&D section WG5 - Snowmass Conference

16 08/18/2005 P. Bauer Materials R&D section WG5 - Snowmass Conference